In a process of producing a semiconductor device, a film to be treated (for example, an insulating film or an electroconductive film) is generally formed on a base material. Subsequently, an etching mask is formed on the film, and a pattern having predetermined dimension and shape is formed by etching in the film to be treated. The above procedure is repeated a plurality of times.
In the step of forming a pattern in the film to be treated, a lithography technique is generally used in which the so-called exposure step, development treatment step and the like are carried out using a photosensitive material called a photoresist (hereinafter referred to simply as “resist”).
When the lithography technique is used, a pattern of the film to be treated is generally formed according to the following procedure. Specifically, a resist film is formed by coating on a film to be treated, and the resist film in its predetermined region is exposed imagewise through an exposure mask (reticle). Next, the resist film after the exposure is developed, and the exposed or unexposed part is removed to form a resist pattern. A pattern of the film to be treated is then formed, for example, by drying etching using this resist pattern as a mask.
In recent years, when a resist film is exposed, short wavelength exposure light should be used, for example, from the viewpoints of improved resolution and throughput. For example, light sources which emit ultraviolet light, such as, KrF excimer laser and ArF excimer laser, are used so as to obtain such a fine pattern as has a line width of about 90 nm. Further, according to the liquid immersion lithography, the line width can be more decreased to about 40 nm.
However, it is difficult to further miniaturize a pattern only by improving the light source and/or method of exposure, and hence novel pattern formation methods are being studied. For example, Patent document 1 discloses a method comprising the steps of: forming a first relief pattern on a film to be treated; coating side walls of ridges in the relief pattern to form a spacer made of polysilazane-containing resin composition; and forming a superfine pattern by use of the spacer or the resin layer around there as a mask. This method (hereinafter, often referred to as “double patterning” for simplification) enables to reduce the line width to about 20 nm.    [Patent document 1] International Patent Publication No. 2009/96371 Pamphlet